Unwind protect for describe key

[andyjda]

As mentioned by tangxinfa in a comment to the original describe-key issue, some times the advice and hook created within the describe-key function are not removed (as would be expected). This can cause errors down the line.
This issue was caused by the fact that

(remove-hook 'help-fns-describe-function-functions
                 #'god-mode--help-fn-describe-function)

was at the end of god-mode-describe-key, without taking into account that, in cases when god-mode-describe-key exits abnormally, this last part is never executed.

The solution is to use the special form unwind-protect which allows us to specify "unwind-forms" that are always executed, even if the body of our function exits abnormally (see the documentation for more details)

[darth10]

Thanks for the quick fix @andyjda!

LGTM, not sure why I didn't think about using unwind-protect earlier.